Activation of T lymphocytes involves a preprogrammed alteration in lymphocyte responsiveness to informational signals transmitted by a variety of regulatory molecules. These signals are channeled to the cell via stereospecific receptor proteins. In studies performed in our laboratory, we have found that the process of human T lymphocyte activation sets in motion a process in which a series of receptor and other functionally important membrane proteins are expressed de novo in a reproducible, non-synchronous manner. The stages of T cell activation can be defined, in large part, by using the sequential de novo expression of functionally important proteins as a roadmap of the activation sequence. We will map the kinetic expression of the phenotypic markers of T cell activation for each subset by use of a multibeam laser activated cell sorter in concert with fluorochrome labelled antibodies, hormones, and growth factors, and stains that detect changes in ion flux and intracellular pH. We will determine the stimuli required to direct T cells from one stage to the next of the activation sequence and hence determine the sequence of signals required for proliferation and activation of the functional program of each subset. These efforts are made possible by our access to cloned cell lines and our ability to purify lymphokines by HPLC. These data should provide a framework by which autoimmune and immunodeficiency states may be dissected and perhaps ameliorated by use of lymphokines. A series of activation antigens of particular interest have been identified by flow cytometric probes (4 monoclonal antibodies and fluoresceinated insulin) these proteins appear on essentially all activated human T cells until cycles of replication cease. These include the transferrin, insulin, and interleukin-2 (IL-2) receptors. The monoclonal antibodies which recognize the IL-2 and another T cell specific activation, respectively, are of special interest. We will ascertain if they neatly define the entire antigen activated T cell population. Universal probes of activation represent an attractive therapy by which to manipulate only those T cell clones that are activated by antigens, particularly as the heterogeneity of therapeutic probes needed is minor as compared to idiotype or anti-idiotype specific agents. Accordingly, the utility of a monoclonal antibody directed against a murine early activation antigen will be tested in vivo for therapy in transplantation, autoimmunity, and lymphoma.